In conventional techniques, an electrical discharge machining in which an electrical discharge is made to occur between a workpiece as an object to be machined and an electrode to machine the workpiece is known. In the electrical discharge machining, a part of the workpiece is melted and removed, thereby being capable of being machined into a desired shape. As the electrical discharge machining, a wire electrical discharge machining in which an electrical discharge is made to occur at an electrical discharge region of a center portion of an electrode linearly extending in a long manner and the linear electrode is moved relative to a workpiece, thereby cutting the workpiece is known. Further, an electrical discharge machining in which, using a rod-shaped electrode, an electrical discharge is made to occur at a tip end of the rod-shaped electrode while the rod-shaped electrode is inserted in the interior of a workpiece, thereby forming a hole in the workpiece is known.
Such an electrical discharge machining is suitable for machining, for example, a workpiece made of a hard material. When the workpiece made of a hard material is subjected to a cutting machining, machining is difficult and a very large number of tools are necessary. On the other hand, in the electrical discharge machining, to melt a part of the workpiece, even the workpiece made of a hard material can be easily machined. In addition, in the electrical discharge machining in which the hole is formed in the workpiece using the rod-shaped electrode, the hole having a very small diameter which is difficult to be formed by the cutting machining can be formed.
Japanese Laid-open Patent Publication No. H5-345228 discloses a machining method in which, from an initial position at which a tool electrode is in contact with a workpiece, the electrode is laterally moved. In this publication, longitudinal wear of a rotation electrode is simulated prior to machining and wear is calculated from a predetermined parameter. Then, advancing the tool electrode while machining the workpiece without lateral wear are disclosed.